Method and apparatus for electrostatic color printing

ABSTRACT

A process of and apparatus for rapidly producing a multicolor print from a multicolor original such as a transparency in which there are carried out successive cycles of operations each of which cycles comprises electrostatically charging a photoconductive surface, exposing the surface to a particular color radiation pattern derived from the original, wetting the surface with clear resistive liquid, and thereafter applying a developing agent to the surface for the particular color being developed during that cycle. The apparatus produces the multicolored copy automatically, and, with but minor changes in the apparatus, the sequence of colors to be developed can be readily changed for successive sequences.

United States Patent [191 Hastwell Jan. 9, 1973 METHOD AND APPARATUS FOR ELECTROSTATIC COLOR PRINTING [75] Inventor: Peter J. Hastwell, Elizabeth Grove,

Australia [73] Assignee: Savin Business Machines Corporation, New York, N.Y.

[22] Filed: June 18, 1970 [21] Appl. No.: 47,273

[52] US. Cl. ..355/4 [51] Int. Cl. ..G03g 15/00 [58] Field of Search ..355/4, 10; 118/239 [56] References Cited UNITED STATES PATENTS 3,420,151 l/l969 Levine et a1 ..355/4 3,130,655 4/1964 3,450,473 6/1969 3,129,115 4/1964 3,574,456 4/1971 Grace ..355/4 Primary Examiner-John M. Horan Attorney-Shenier and OConnor 57 ABSTRACT A process of and apparatus for rapidly producing a multicolor print from a multicolor original such as a transparency in which there are carried out successive cycles of operations each of which cycles comprises electrostatically charging a photoconductive surface, exposing the surface to a particular color radiation pattern derived from the original, wetting the surface with clear resistive liquid, and thereafter applying a developing agent to the surface for the particular color being developed during that cycle. The apparatus produces the multicolored copy automatically, and, with but minor changes in the apparatus, the sequence of colors to be developed can be readily changed for successive sequences.

29 Claims, 25 Drawing Figures Pmmmm 9 m3 sum 0 1 or 16 INVENTOR Pater I H057'Wg// HT TORN Y5 PAIENIEnm ems 3,709,594 SHEET 030! 16 INVENTOR Pefer I Hasfwe/l l ATTORNEYS- PATENTEDJAN 9 ms SHEET USDF 16 MXM HTTORNEYS PATENTEDJAN 9 I975 SHEET O7UF 16 Source MZM H T TORNEYS PATENTED JAN 9 I973 SHEET 09 0F 16 INVENTflR Pefer I Hasfwefl wffi wr HTTORNEYS PAIENIEUJAI ems 3,709,594 sum 11m 16 IN VEN TOR PeT r HasTwe/l 4 TTORNE Y5 PATENTEDJMI 9 ma SHEET l HJF 16 fil/ll/ll/l/ INVENTOR Pefer J Hasfwe/l ATTORNEYS PATENIEDJAN 9191s 3.709.594 sum 15m 1s INVENTOR fsfer J Hasfw'el/ MA n rranws vs PATENTEUJAN 9 ma SHEET IBUF 16 "Wm ml okm mEm 4mm c m mmh ik mznkou Qua vum mvslvrbp Pefer J Hash e HTTORNEYS METHOD AND APPARATUS FOR ELECTROSTATIC COLOR PRINTING BACKGROUND OF THE INVENTION filtered pattern of radiation to form a latent electrostatic image, applying a colored developing agent and repeating the sequence with different colors as necessary.

With this known state of the art, the problems encountered in rapidly, efficiently and inexpensively processing color prints of high quality have not been resolved. Color printing requires exact or closely controlled registration of onecolor with respect to the others to provide quality prints. Further, the process of successively exposing the photoconductive layer to various color components of the image to be reproduced has not heretofore been successfully implemented due to the complexity of the problems involved and due to the many variables implicit in this intricate art. For example, attempting to overcome one problem such as fatigue of the photoconductor may give rise to another problem such as failure to overprint fully. Another problem is the removal of excess liquid from the surface being developed during development.

l have invented a system for producing color prints by an electrostatic process which overcomes the defects of systems of the prior art. My process and apparatus produces such prints in a rapid, expeditious and relatively inexpensive manner. My system overcomes both the problem of photoconductor fatigue and of failure to overprint fully. It effectively solves the problem of removal of excess liquid during development.

SUMMARY OF THE INVENTION The major object of my invention is to provide a process for electrophotographically producing color prints of high quality.

Another object of my invention is to provide an electrophotographic machine for automatically producing high quality and inexpensive color prints.

A further object of my invention is to provide a machine for producing a color print electrophotographically by means of an automatic cycle of operations which can be controlled to a high degree of sensitivity. v

A still further object of my invention is to provide an automatic sequencing machine for providing color copies electrophotographically in which the color sequence can be readily changed.

Other and further objects of my invention will appear from the following description.

In general my invention contemplates the provision of a process of and apparatus for producing color prints from a transparency or the like in which the print material is successively carried through a plurality of cycles, each of which includes charging the photoconductive surface of the material, exposing the charged surface to one of the component colors of the original, wetting the exposed surface with clear resistive liquid, and then developing the image of that color.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings which form a part of the instant specification and which are to be read in conjunction therewith and in which like reference numerals are used to indicate like parts in the various views:

FIG. 1 is a front perspective view of a machine in accordance with a first embodiment of the invention, the exterior housing of the machine having been removed to show the interior thereof;

FIG. 2 is a sectional view taken along line 2-2 of FIG. 1;

FIG. 3 is a sectional view taken along line 3-3 of FIG. 1;

FIG. 4 is an exploded perspective view of a wetting liquid tray as used herein;

FIG. 5 is a schematic view of one form of control circuit which may be employed in the form of my invention shown in FIGS. 1 to 4.

FIG. 6 is a block diagram of the sequence of steps of the embodiment of my invention shown in FIGS. 1 to 4.

FIG. 7 is a schematic view of the developer particle size control system for the developing tray of FIG. 4;

FIG. 8 is an exploded perspective view of an alternative form of developer tank;

FIG. 9 is a schematic view, of one form of a wetting agent filtration system for a wetting agent tray of FIG.

FIG. 9a is a schematic view of an alternate filter member for the system of FIG. 9;

FIG. 10 is a front elevation of the interior of an alternate form of my apparatus with parts broken away and with other parts shown in section;

FIG. 11 is a side elevation of the apparatus shown in FIG. 10 taken along line llll of FIG. 10;

FIG. 12 is a schematic view of one form of control circuit which may be used in the form of my invention shown in FIGS. 10 and 11;

FIG. 13 is an exploded perspective view of one form of developing tray of the embodiment of my apparatus shown in FIGS. 10 and 11;

FIG. 14 is a side elevation of the copy material clamping mechanism of the embodiment shown in FIGS. 10 and 11 with the parts thereof in released condition;

FIG. 15 is a side elevation of the copy material clamping mechanism with the parts in clamping position;

FIG. 16 is a perspective view of a corona unit and a wetting unit of the form of my apparatus shown in FIGS. 10 and 11;

FIG. I7 is a perspective view of a third embodiment of my invention with the housing thereof partially broken away;

FIG. 18 is a fragmentary view of the form of my apparatus shown in FIG. 17 illustrating the interaction between the paper carriage and the wetting unit during the prewetting step;

FIG. 19 is a fragmentary view of the form of my apparatus shown in FIG. 17 illustrating a developing step;

FIG. 20 is an end elevation of the apparatus shown in FIG. 19, with a part shown in section and with other parts broken away;

FIG. 21 is a fragmentary view of the form of my machine shown in FIG. 17 illustrating the after-wetting and drying actions thereof;

FIG. 22 is a fragmentary view of the developer of the form of my apparatus shown in FIG. 17 illustrating my developer tank stabilizing system;

FIG. 23 is a perspective view of one form of electrostatic filtering system which I may employ in the form of my invention illustrated in FIGS. 17 and 18;

FIG. 24 is a schematic view illustrating one form of control system which I may employ in the form of my apparatus illustrated in FIG. 17.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIGS. 1 to 3 the first embodiment of my electrostatic copying machine, indicated generally by the reference character 10, normally is encased in an opaque housing, (not shown). A carriage, indicated generally by the reference character 12 supports the projector, the copy paper and the paper feed system, to be described in detail hereinbelow. The carriage 12 is translatable along a linear travel path transversely of the machine past a bank of processing stations indicated generally by the numeral 14, and disposed between the side walls 16 of the machine 10.

Carriage 12 includes a front wall 18, a back wall 20 and side walls 21. Respective pitch chains 22 extending around sprocket wheels 24 on the machine frame are connected to the carriage 12 so as to move the carriage across the machine on guide rails 26 when the chains are driven in a manner to be described.

A bracket 28 secured to the wall 20 carries a roll 30 of copy material 34. From the roll 30 the copy material extends over a paper length measuring roll 42 under a guide roll 44, through the space between an exposure window 36 and a vertically shiftable clamping pad 38, under a guide roll 37 through the nip between feed rolls 48, and through the space between a rotary cutting blade 51 and a stationary cutting blade 52 to an outlet slot 50 in front wall 18.

Respective shafts 32 supported by side walls 21 adjacent the front of the carrier 12 carry supplies of blotting material 35 lengths of which extend under the guide rolls 37 and 44 and under clamping pad 38 over the edges of the material 34 to take-up rolls 40 on side walls 21. As will be explained more fully hereinbelow in operation of my machine a solenoid 39 is actuated to move pad 38 downwardly to move the blotting material into engagement with the copy material edges to remove any developer which tends to flow over the edges of the copy material during development. Suitable clutches are provided for the feed rolls 48 and for the rotary paper cutter 51. The clutches are controlled by the control circuit to be described hereinafter and by operationof measuring roll 42.

Carriage 12 also supports the projection and exposure unit, indicated generally by the reference character 60 of my system. Owing to the fact that the exposure system and the paper transport system are mounted on the same carriage proper registry of the image produced by the projection system with an already developed image on the copy material is ensured.

The unit 60 includes a projector 70 mounted on the base 62 of carriage l2. Projector 70 may be a slide projector of known design in which a holder 77 supports a transparency to be copied between a lamp 72 and a lens 74.

While the invention is described as utilizing transmission through a transparency, it can be understood that the principles set forth apply equally to systems with light reflected from the surface coloration of an image.

The radiation pattern emitted through the lens is directed towards the outer annulus of an optical filter wheel 80. This filter wheel has its outer annulus comprising a series of angularly spaced color filter screens, each filter screen being of a different color. By stepping wheel 80 in a manner to be described to position various filter segments in front of the transparency, the portion of the color spectrum transmitted from the transparency can be varied. The filter wheel 80 may be stepped angularly through an arc of proper length by a solenoid or a motor 82 to position successive filters in the line of transmission from lens during successive projection periods.

The radiation pattern transmitted through a filter strikes the surface of an inclined mirror 84 on base 62 and is reflected upwardly toward the length of blank copy paper 34 resting on window 36.

As has been pointed out hereinabove the ends of chains 22 are attached to carriage 12. A reversible drive motor 66 is adapted to be energized to drive a shaft carrying sprocket wheels 24 at the left of the machine as-viewed in FIG. 2 to move carriage 12 back and forth between limits defined by switches 67 and 68. In FIG. 2 the left hand limit position of carriage 12 is shown in full lines and the right hand limit position thereof in broken lines.

The bank 14 of color processing units is located intermediate the limit positions of the carriage 12 at a height between the mirror 84 and the window 36. The side walls 21 of the carriage 12 are so shaped as to permit the bank 14 of units to move through this space as the carriage reciprocates. As viewed from right to left in FIG. 2 bank 14 includes a corona charging unit 101, a wetting unit 102, a group of developing units 103 to 106 corresponding to four different colors, another wetting unit 107, and another corona unit 108.

The charging units 101 and 108 each include corona wires normal or approximately normal to the travel path of the carriage structure 12. The charging wires at both stations 101 or 108 are connected in parallel to a high voltage direct current source, each charger being connected to the negative source lead, while the conductive layer of the paper length 34 is connected to ground. When one of the chargers is energized individually by the high voltage direct current source, the charger emits an electrostatic charging corona to apply a charge to paper 34, as is well known in the art.

Referring now to FIG. 8 I have shown one form of as sembly which may comprise the unit 102, for example. Tank 122 has ends 124 provided with bearing journals 128 for receiving semicircular bearings 130 which pivotally carry rollers 126 formed of any suitable material such as rubber or aluminum or the like. Tank 122 is filled with a resinous liquid insulating material to such a level that rollers 126 are partially immersed in the liquid. As the copy material passes over the tray 122 in contact with rollers 126 the latter rotate to apply liquid to the underside of the material 34. Solenoids 162 to 167 associated with the respective units 102 to 107 are adapted selectively to be energized to raise the corresponding tray in a manner to be described to bring rollers 126 to positions at which they will engage the material 34 or the carriage 12. Any suitable means such as vertically extending pins 132 may support the tank 122 as it is lifted by the solenoid 162 or 167.

l have discovered that in the course of development of successive images without full drying of the material 34 some toner may find its way into the prewetting liquid in tank 122. The obvious disadvantage in such a circumstance is the application of toner to the material 34 in the course of the prewetting operation. Referring to FIG. 9, I may provide a filtration and recirculation system for the wetting liquid in trays 122. A drain tube 185a passes wetting liquid from the wetting tray 122 to a filler chamber 186a formed from insulating material. A mass of steel wool 188a or other large surface area conductor within the chamber 186a is connected to the negative terminal of the high voltage direct current supply 190. A pump 192a removes liquid from chamber 186a through a line 191a and delivers it to tray 122 through a tube 194a.

By imposing this high voltage on the large surface area conductor 188a, any toner particles carried into the circulated wetting liquid will precipitate onto the charged conductor and will be held there. I have found that the liquid provides sufficient grounding to eliminate the need for a connection from the positive or ground lead of source 190 to chamber 186.

Referring now to FIG. 9a as an alternative to the system of FIG. 9, I use a conductive cylinder 195a to which the inlet 185a and the outlet 191a are connected. A cylindrical mesh conducting screen 196a is spaced from the wall of cylinder 195a by insulators 197. The mesh screen 196a is connected to the negative lead of a low voltage (30 volt d.c) source 198, while the cylinder 195a is connected to the positive terminal. The low voltage causes toner particles carried in the liquid to be attracted to the mesh screen and the clean liquid will be pumped back to the wetting tray.

While I might use the construction shown in FIG. 8 for the developing units 103 to 106, preferably 1 employ the construction illustrated in FIG. 4 in which l have shown the details of construction of the unit 103, for example. Each of the units such as the unit 103, comprises a generally rectangular tray 140 for receiving developer liquid. Blocks 142 adjacent the sides of the tray are formed with vertically extending slotted bores 144 for slidably receiving bearings 146 which rotatably receive the shaft ends of rollers 148. Springs 150 in bores 144 below the bearings 146 resiliently urge the bearings upwardly in bores 144 to position the upper portions thereof out of the liquid and into contact with the material 34 passing by the station.

Preferably l form the rollers 148 from anodized aluminum or the like and l serrate or knurl the surfaces thereof. 1 further so arrange the rollers 148 as to have progressively decreasing diameters in the direction of movement of the copy material past the unit. Anodizing the rollers produces an insulating surface thereon while the surface knurling ensures good distribution of the developer. Although the rollers are of different diameters they are so spring loaded that a plane in the path of movement of the copy material is tangent to all rolls. Positioning of the smallest roll last in the direction of movement of the copy material during developing provides a wiping action which leaves the material relatively dry after development.

Preferably 1 position a sponge or polyurethane foam pad on spacers 162a on the bottom of each tray. The pad of foam has a sloping upper face to maintain contact with the underside of each of the rollers 1460f the tray. I maintain the developer liquid at a level adjacent the top of the pad 160 to saturate the pad and keep a supply of liquid toner in contact with the rollers at all times.

From the structure just described it will be seen that, with a developing tray in its raised position, as the carriage 12 moves thereby the rollers are rotated by contact with the material 34 to carry developer out of the tray and to deposit the liquid on the photoconductive layer in accordance with the latent electrostatic image thereon. By the use of a large number of small diameter rollers, each roller contacts only a small portion of the image in the course of a revolution and each portion of the copy is contacted by at least one roller during development. As a result, no undesirable blank spots are produced in the developed copy such as otherwise might result if the roller system were such that a portion of the surface thereof which had already developed one area were then required to develop a following area of the copy material before the roller completed a revolution. By the use of rollers of different diameters, a more random distribution of developer takes place, insuring that the entire latent image is developed.

It may be desirable to bias the developer rolls. For example, a voltage of from 2.0 volts to 5.0 d.c. volts may be applied between the body of the rollers 148 and the conductive backing of the photoconductive paper, the negative voltage terminal being connected to all of the rollers 148 in any suitable fashion. Such a bias voltage aids in the removal of excess developer.

Referring now to FIG. 7 l have shown a system for inhibiting agglomeration of toner particles in the developer. Such a system may be applied to all developer units. Agglomeration of toner particles produces a coarseness or graininess in the developed copy and prevents production of copies with fine gradations in density or contrast.

in the system illustrated in FIG. 7 a drain tube conducts developer liquid from tray 140 to the toner supply bottle 172 through a stopper 174 in the mouth of the inverted supply bottle 172. An overflow tube 175 leads from tray 140 at a level adjacent the top of sponge 160 to the inside of the bottle 172 at a location above the normal level of liquid therein. A pump 178 draws liquid from bottle 172 through a tube 176 and feeds the liquid through a line 179 to an agitator 180 the outlet of which is connected to the interior of tray 140 by a line 181. Agitator 180 may, for example, be a wedge jet-edge whistle of the type shown on pages l30l32 of Ultrasonics (2nd Edition 1960) by Benson Corlin, published by McGraw Hill, New York, NY. The agitator 180 when energized produces internal cavitation to disperse the particles in the liquid and reduce the average particle size.

I employ a comparatively small diameter tube 170 as my drain tube so that the amount of liquid fed to the 

2. Apparatus for producing a color print of a multicolor original including in combination a carriage supporting a length of photoconductive copy material, a plurality of normally inactive developer applicator units, means for reciprocating said carriage along a generally straight line path above said units past said units in a plurality of cycles, respective means mounting said developer units for movement between inactive positions in said line and active positions adjacent to said path to apply developer to copy material on said carriage as it moves past the unit, means for applying a uniform charge over the surface of said material in the course of each of said cycles, means for exposing the charged surface to an image of said original in each of said cycles to produce a latent electrostatic image on said surface, and means for selectively moving said developer applicator units from inactive to active to active position during the movement of said carriage past the unit on the respective cycles.
 3. Apparatus as in claim 2 in which said moving means comprises a rotary carrier, means mounting said units in spaced relationship around the periphery of said carrier, means mounting said carrier for rotary movement around an axis below said path and means for stepping said carrier through the distance between adjacent units on each of said cycles.
 4. Apparatus as in claim 2 in which each of said developer applying units comprises a tray for holding developer liquid, a plurality of applicators and means biasing said applicators outwardly of said tray.
 5. Apparatus as in claim 4 in which said carriage comprises means for acting on said applicators against said biasing means to position said applicators out of engagement with but closely adjacent to said copy material.
 6. Apparatus as in claim 4 in which said applicators comprise rolls.
 7. Apparatus as in claim 6 in which said rolls have roughened surfaces.
 8. Apparatus as in claim 6 in which said rolls have different diameters.
 9. Apparatus as in claim 2 in which said exposing means comprises a projector supported on said carriage, a filter comprising a plurality of sections of various colors supported on said carriage and means for stepping said filter.
 10. Apparatus as in claim 2 in which said exposing means comprises a projector supported on said carriage for movement therewith and respective steppable filters at each side of said plurality of developer applicators.
 11. Apparatus as in claim 2 in which said exposure means comprises a stationary projector at one side of said developer applicator units and a steppable filter adjacent said projector.
 12. Apparatus as in claim 2 including a wetting unit mounted in said path.
 13. Apparatus as in claim 12 including a precipitator associated with said wetting unit.
 14. Apparatus as in claim 2 including clamping means on said carriage for holding said copy material during operation of said machine.
 15. Apparatus as in claim 2 including means for removing excess liquid from said copy material after a developing operation.
 16. Apparatus for electrostatically developing a color print from a multicolor original including in combination, a carriage for supporting a length of copy material, means mounting said carriage for movement along a generally straight linear path, a charging station and an exposure station and wetting station and a developing station at spaced locations along said path, a charging unit at said charging station, means for selectively exposing said length to an image of said original through filters of various colors at said exposure station, a wetting unit adjacent to said path at said wetting station, said wetting unit adapted to be activated to apply wetting liquid to said length as said carriage passes said wetting unit, a plurality of developer units, means mounting said units at said developer station in a line below said path for movement into said path, means for reciprocating said carriage along said path, and means for selectively raising said developer units into said path.
 17. Apparatus as in claim 16 in which said charging unit is located at one end of said line, said apparatus including a second charging unit at the other end of said line.
 18. Apparatus as in claim 16 in which said charging unit is located at one end of said line, said apparatus including a second charging unit at the other end of said line and respective wetting units including said first named wetting unit disposed in said line between said charging units and said developer applying units for movement into and out of said path.
 19. Apparatus for producing a color print from a multicolor original including in combination, a carriage supporting a length of copy material, means mounting said carriage for movement along a generally straight path having a developer station intermediate the ends thereof, a rotary carrier, a plurality of developer applying units carried by said carrier, means mounting said carrier adjacent said path for rotary movement successively to position said developer units in an active position in said path to apply developer to copy material on said carriage passing through said developer station, a steppable multicolor filter adjacent said carrier, a projector for illuminating said copy material with an image of said original through said filter, a charging unit in said path adjacent said carrier, means for stepping said carrier, means for stepping said filter, means for driving said carriage and means for actuating said charging unit and said projector and said stepping means and said driving means in timed relationship to cause the developer unit in active position to apply developer to said copy material in the course of movement of said carriage through said developer station.
 20. Apparatus as in claim 19 in which said projector is on said carriage, and in which said filter is at one side of said carrier, said apparatus including a second steppable filter at the other side of said carrier.
 21. Apparatus as in claim 19 including a wetting unit between said charging unit and said carrier.
 22. Apparatus as in claim 19 in which each of said developing units comprise a tray pivotally supported on said carrier, said apparatus including means for maintaining said trays level as said carrier rotates.
 23. Apparatus as in claim 19 including means forming an exposure window on said carriage and actuatable means for releasably clamping said copy material in position over said window.
 24. Apparatus as in claim 16 in which said wetting unit comprises a tray containing wetting liquid, a pair of applicators, means biasing said applicators into said path, and means on said carriage for moving said applicators against the action of said biasing means to positions out of but closely adjacent to said path whereby said liquid is applied to said copy material by surface tension.
 25. Apparatus as in claim 24 including a circulating system for supplying clear electro-resistive liquid to said tray, and an electrostatic precipitator in said circulating system.
 26. Apparatus as in claim 24 including a wiper blade associated with one of said applicators and means responsive to movement of said carriage in one direction for moving said blade out of engagement with said applicator and responsive to movement of said carriage in the other direction for moving said blade into engagement with said applicator.
 27. ApparAtus as in claim 24 including a blotter roll, means mounting said blotter roll for movement into and out of said path, means biasing said blotter roll into said path and means responsive to movement of said carriage in one direction for moving said roll out of said path during the initial portion of movement of said carriage thereby and for releasing said roll during the terminal portion of the movement of said carriage thereby.
 28. Apparatus as in claim 27 including means for directing a stream of air against said copy material as it approaches said blotter roll in said one direction of movement.
 29. Apparatus as in claim 25 in which said precipitator comprises a plurality of plates of conductive material and zinc oxide coated material on the surface of certain of said plates. 